Previous work has shown that the organic material related to the enamel crystals can be visualized by electron microscopy in thin sections of enamel demineralized by floating on phosphotungstic acid. Whether this enamel material is a preformed structure involved in crystal nucleation and orientation or represents organic material adsorbed to the surface of the crytals is unresolved. The purpose of the present study is to further characterize the structural relationship between enamel matrix material and the enamel crystals, and to obtain basic information on the nature of the organic material.